The degree of tension or stress on a heart muscle fiber as it contracts is termed the after load. Because pressure within the ventricles rises rapidly from a diastolic to a systolic value as blood is pumped out into the aorta and pulmonary arteries, the part of the ventricle that first contracts due to an excitatory stimulation pulse does so against a lower after load than does a part of the ventricle contracting later. Therefore, after load is the end load against which the heart contracts to eject blood. Many factors may influence the after load, one of which is the aortic pressure the left ventricular muscle must overcome to eject blood. A higher aortic/pulmonary pressure increases the after load on the left/right ventricle, respectively. The tension on the muscle fibers in the heart wall is the pressure within the ventricle multiplied by the volume within the ventricle divided by the wall thickness according to Laplace's law. This ratio is another factor used in determining the after load. By applying pressure on certain portions of the heart, after load can be greatly reduced or eliminated.
Prior art devices which attempt to address the aforementioned problems include pump-devices which surround certain portions of the heart to stimulate the portions. Other prior art devices include components that cross the pulmonic and tricuspid valves in order to stimulate the pulmonary artery.
Some other methods of attempting to modulate after load may include an extra-aortic balloon pump enabled to encircle the ascending aorta. This requires dissecting the aorta free from the pulmonary artery, which it abuts.